The unconfined compression test is derived from the triaxial compression test.

Triaxial compression tests involve subjecting a cylindrical soil sample to a controlled stress condition. The sample is confined laterally with a rubber membrane and loaded axially. The axial load is gradually increased until failure occurs. This test is used to determine the shear strength parameters of the soil, such as the cohesion and friction angle.

The unconfined compression test is a simplified version of the triaxial compression test. In this test, the soil sample is not laterally confined but is loaded axially until failure. The test is conducted on undisturbed or remolded soil samples.

Here is a detailed explanation of why the unconfined compression test is derived from the triaxial compression test:

1. Basis of the triaxial compression test:
- The triaxial compression test is widely used to determine the shear strength parameters of soils.
- It provides valuable information about the stress-strain behavior of the soil and its strength characteristics.

2. Simplification of the testing procedure:
- The unconfined compression test is a simplified version of the triaxial compression test.
- It eliminates the need for lateral confinement of the soil sample, making it easier and less time-consuming to perform.

3. Similar loading conditions:
- Both tests involve loading the soil sample axially until failure.
- The axial load is gradually increased until the sample reaches its peak strength and eventually fails.

4. Shear strength determination:
- The unconfined compression test allows for the determination of the undrained shear strength of the soil.
- Undrained shear strength refers to the shear strength of a soil sample when it is loaded rapidly and without the dissipation of excess pore water pressure.
- The undrained shear strength is a crucial parameter in geotechnical engineering design.

In summary, the unconfined compression test is derived from the triaxial compression test by simplifying the testing procedure and eliminating the need for lateral confinement of the soil sample. Both tests involve subjecting the soil sample to axial loading until failure and provide valuable information about the shear strength characteristics of the soil.